The parents of Damilola Taylor finally witnessed justice for their son yesterday when two teenage gang members were convicted of his killing six years ago after a £16m investigation blighted by mistakes and setbacks.

Police across the country are reviewing scores of murders in case failures in the government-run forensic science laboratory, which were exposed in the trial, have let killers remain free.

The Home Office is investigating how two scientists at the forensic lab missed the vital spots of Damilola's blood that could have brought his killers to justice much sooner.

Moments after Ricky Preddie, now 19, and his brother Danny, now 18, were convicted of the stabbing yesterday, the 10-year-old victim's father, Richard Taylor, expressed his relief.

"We, the family, feel nobody can ever return our son to us, but it is a great comfort that justice has finally been done for Damilola," he said. "We pray that his gentle soul can now rest in peace."

Raged in the dock

After six years, two police inquiries and three trials which cost an estimated £16m, it took an Old Bailey jury six hours and 20 minutes to find the Preddies guilty of manslaughter.

The boys, members of a south London gang, the Young Peckham Boys, raged in the dock as they were led down at the Old Bailey. "You're corrupt ... you must be mad ... you know nothing," said Ricky Preddie, who was 13 at the time of the killing.

After being ordered down to the cell by the judge. Mr Justice Goldring, Ricky's shouting could still be heard. Danny, who was 12 at the time, looked stunned as he tried to calm his brother.

The boys, both of whom were supposedly under supervision at the time of Damilola's killing, were remanded in custody for reports before sentencing. The maximum sentence is life.

Although the Preddies were prime suspects within days of the stabbing, they were dropped from the inquiry because of the lack of forensic evidence. Instead police charged four other members of their gang. They were acquitted in 2002 after a key witness, a 13-year-old girl, was exposed as a liar.

A new police inquiry discovered that two spots of Damilola's blood on a shoe belonging to Danny Preddie and a sweatshirt belonging to his brother had been missed by two scientists within the forensic lab six years ago.

The Preddies were rearrested and charged last year with murder. But a jury failed to reach a verdict and the crown pursued the third trial on manslaughter charges alone. The defence counsel argued that the forensic evidence could have come from contamination. Orlando Pownall QC, for Danny, said it was planted by police. But the jury believed the prosecution that the Preddies and other members of their gang had surrounded Damilola and stabbed him with a broken bottle as he walked home in November 2000.

Commander Dave Johnston, of the Metropolitan Police specialist crime directorate, said he was dismayed that crucial evidence in the case was not found sooner.

He said: "Clearly the forensic evidence was particularly involved in bringing justice and had it been found sooner we would have seen this played out a lot quicker."

Damilola was attacked as he walked to his home on the rundown north Peckham estate in south London from an after-school computer club.

Images caught on CCTV of him skipping home in a silver jacket were shown repeatedly in the media as Scotland Yard set in train an investigation they hoped would wipe away the stain of institutional racism given to them by the Macpherson inquiry after the failures in the Stephen Lawrence investigation.

Damilola had come to Britain with his mother Gloria from his home in Nigeria to seek medical treatment for his older sister. But after growing up in one of the most violent countries in the world, he fell victim to the growing culture of knives and stabbings in the streets of south London.

Throughout the long wait for justice the Taylors have remained loyal to the Met, and Mr Johnston praised them yesterday for their fortitude.

But the revelations in the case about the failures within the forensic lab, which is used by police forces across the country, could have ongoing and severe implications.

The Home Office minister Joan Ryan said yesterday that a review of what happened was necessary.

New evidence

"In view of issues around forensic evidence that emerged during this trial, I have decided that an independent review of this case be carried out.

"The Board of the Forensic Science Service is in full agreement with this decision. The review will be led by a QC and leading forensic scientist and will report in the autumn."

John Yates, one of the deputy assistant commissioners of the Met, said his officers were looking at a number of cases, in which suspects had either not been charged or were charged and not convicted and were now at liberty, with a view to resubmitting evidence for new forensic testing.

"These are the type of cases we are looking at. They are cases where you would expect to find a transfer of bodily fluid and there wasn't any found," he said. "We will be looking at murders and serious crimes."

He said the review could involve several cases if it was found that the failings within the forensic lab were systemic.

If police do uncover forensic evidence that has been overlooked in any of the cases they are likely to face a battle to bring any suspects to justice. Defence lawyers are likely to challenge prosecutions on the basis that evidence could have been contaminated within the laboratories in the years since the original inquiries.

Police refused to name any of the cases that are under review.

Chronology

2000

Nov 27 Damilola Taylor dies after he is stabbed in the thigh with a broken bottle on a stairwell of the North Peckham estate.

Dec 2 Several youths arrested, including Danny and Ricky Preddie. All released without charge.

Dec 14 Preddies rearrested with nine other youths. No charges.

2001

Jan 19 Damilola's funeral.

Jun 26 Four youths, not including the Preddies, charged with murder.

2002

Jan 30 Trial of four youths begins.

Feb 4-12 Prosecution's star witness, a 14-year-old girl named as Bromley, tells Old Bailey jury how she witnessed attack on Damilola. She is branded a liar and case collapses.

2003

Nov 27 Police announce review of all evidence, using new forensic techniques.